Method of producing steel



Patented Feb. 15, 1938 UNITED STATES PATENT OFFICE No Drawing.

Application March 11, 1936,

Serial No. 68,345

7 Claims.

The invention relates to the manufacture of rimming steels and has particular reference to improvements in the method of producing ingots from said steels.

Standard rimmed ingots are produced by allowing the ingot to effervesce, which is generally referred to as "rimming, during solidification in the mould after pouring. Initial solidification of the ingot is practically coincident with the entrance of the metal into the mould and is due to the contact of the molten metal with the relatively cool walls of the mould. This produces a shell or rim around the ingot, which increases in thickness during the rimming and cooling period while the ingot is solidifying inward toward the core. As solidification continues the impurities are driven inward and upward producing an ingot having a rim of physically sound steel, and which contains less impurities and is therefore 20 more ductile than the core or interior of the ingot. It is usual for the rim to be lower in chemical analysis than the particular heat poured, whereas, the core or interior of the ingot, particularly the upper portion thereof, is character- 25 ized by excessive segregation and numerous large inclusions. For this reason it is general practice throughout the steel industry to apply only the lower sixty per cent of the ingot, when the rolled product therefrom is to be subjected to severe cold forming and drawing, since defects in the steel known as banding, laminations, and breakage occurring during the forming and drawing operations are largely caused by inclusions and segregation. 35 A more recent manufacturing practice in the production of rimmed ingots consists of adding shot aluminum or other suitable deoxidizers to the ingot after pouring, for the purpose of controlling the depth of rim and minimizing segregation. The addition of aluminum or other deoxidizers acts as a killing agent that unites with the oxygen present in the ingot and stops all further rimming action.

Ingots produced as abovedescribed likewise have a shell or rim of steel similar to that formed in standard rimmed ingots, but are particularly characterized by a core or interior representing a decided improvement over that of standard rimmed ingots, from the standpoint of segregation.

An object of the invention resides in the pro duction of ingots and rolled products which will be characterized by the desirable surface properties of standard rimmed steels, and which will represent a further and decided improvement as to interior uniformity over standard rimmed steel grades.

Another object of the invention resides in the production of a superior grade of steel which will excel those heretofore manufactured and particularly to the production of ingots having a rim of physically sound steel of the'desired thickness and a core relatively uniform in chemical composition and characterized by a marked reduction in segregation.

A further object resides in an improved manufacturing method which will represent a considerable saving in the production of ingots in that approximately eighty to eighty-five per cent of the ingot can be utilized for rolling purposes and for cold reduction.

According to the method of the invention the ingot is poured in the usual manner and rimming is allowed to take place for a period of time sufiicient to produce the desired thickness of rim. In general the invention contemplates a rimming action of from one to eight minutes, depending upon the size of ingot and chemical composition of the steel being poured but in its broadest aspect the invention is not limited to the periods stated which are to be taken as merely illustrative for certain grades of steel. By varying the time of the rimming action any desired thickness of rim can be secured and which in chemical composition will approximate very closely that of the heat from which the ingot is poured. The next step in the present manufacturing method consists in the introduction of shot aluminum into the upper portion of the ingot and the proportions may range from approximately three-quarters to one and one-quarter pounds of aluminum per ton of metal. In the preferred practice this aluminum may be intimately associated with the steel by agitating the upper surface of the ingot. Aluminum and other well known deoxidizers such as silicon may be used.

The addition of aluminum kills the steel in the upper portion of the ingot only, since the deoxidizer is not forced down into the body of the ingot but is purposely confined in accordance with the invention to the upper portion thereof, and more particularly to the top four to six inches of the ingot. The killing of the steel in the upper portion of the ingot prevents the escape of the gases from the interior.

In a heat having .06% carbon, 33% manganese, 006% phosphorus, .025% sulphur and .01% silicon, one and one-fourth pounds of aluminum shot was added per ton after the ingots had rimmed for five minutes. The tests of slabs taken from 55 the ingots disclosed a marked reduction in chemical segregation as compared to that in standard rimmed ingots i'rom the same heat. In other words, analysis of the steel found in the center of the ingots disclosed relatively uniform percentages oi! carbo manganese, phosphorus and sulphur. The ingot was characterized by a relatively thin outer layer of steel, substantially uniform in chemical composition throughout, and which approximated very closely that of the heat. The absence or gas h'oles between the rim and core was also clearly evident.

As a result or the solidification oi the ingot in a direction inward toward the core the evolution of the gases continues inward and within the interior o! the ingot. Of course, gases are given 01! after the ingot has been capped according to the invention but the gases do not escape from the surface as in the case of standard rimmed ingots but are confined to the mass of metal interiorof the ingot, that is, within the rim and below the cap. Just what happens to the gases evolved within the ingot after capping thereof can not be stated definitely but it seems probable that the gases are mostly absorbed by the metal. At least the noticeable absence of gas holes of material size and the minute blow holes which are visible upon close inspection of the core substantiates the statement that the gases which have not been absorbed are dispersed uniformly throughout the interior or core of the ingot. Chemical segregation in the core is also reduced to a marked ex tent since upon analysis the steel found in the center will show relatively uniform percentages of carbon, phosphorus and sulphur, which, however, will be higher than that present in the rim. Steel from an ingot produced in accordance with the present invention has been found satisfactory for cold reduction in that banding and laminations are practically eliminated due to the marked decrease in segregation. Also it has been possible to utilize the lower eighty per cent of the ingot for cold reduction and even as high as the eightyfive per cent line has shown good characteristics.

What is claimed is:

l. The method of producing an improved grade of rimmed steel which comprises pouring steel of rimming qualities into an ingot mould, allowing said ingot to naturally cool for a period of time to produce the desired thickness of rim, add ing a deoxidizing agent to the metal in the upper portion of the ingot only, to stop rimming action, and then allowing the ingot to completely soldify.

2. The method of producing an improved grade of rimmed steel which comprises pouring steel of rimming qualities into an ingot mould, allowing said ingot to naturally cool for several minutes to produce the desired thickness of rim, adding a deoxidizing agent to the metal in the upper portion of the ingot only, and stirring to intimately mix the deoxidizing agent and metal to stop rimming action, and then allowing the ingot to completely solidity.

3. The method oi producing an improved grade of rimmed steel which comprises pouring steel of rimming qualities into an ingot mould, allowing said ingot to rim for a period oi! time which may vary from one to eight minutes depending upon the size of the ingot poured, chemical composition of the steel being poured, and thickness of rim desired, adding a deoxidizing agent to the metal in the upper portion of the ingot only, to stop rimming action, and then allowing the ingot to completely solidify.

4. The method of improving the quality of rimming steel which comprises pouring steel of rimming qualities into an ingot mould, allowing said ingot to rim for a period of time which may vary from one to eight minutes depending upon the size of the ingot poured, chemical composition of the steel being poured, and thickness of rim desired, adding a deoxidizing agent to the metal in the upper portion of the ingot only, to stop rimming action, and then allowing the ingot to completely solidify.

5. The method of improving the quality of rimming steel which comprises pouring rimming steel into an ingot mould, allowing said ingot to rim for a period of time to produce the desired thickness of rim, adding shot aluminum to the metal in the upper portion of the ingot only, stirring the metal in the upper portion to intimately mix the same and said shot aluminum, to stop rimming action, and then allowing the ingot to completely solidify.

6. The method of improving the quality of rimming steel which comprises pouring rimming steel into an ingot mould, allowing said ingot to rim for a period of time to produce the desired thickness of rim, adding shot aluminum to the metal in the upper portion of the ingot only in proportions approximating three-quarters to one and one-quarter pounds of aluminum per ton of metal depending upon the chemical composition of the steel being poured, to stop rimming action, and then allowing the ingot to completely solidify.

'7. The method of improving the quality of rimming steel which comprises pouring rimming steel into an ingot mould, allowing said ingot to rim for from one to eight minutes depending upon the size of the ingot poured, chemical composition of the steel being poured, and thickness of rim desired, capping said ingot by-adding shot aluminum to the metal in the upper portion of the ingot only in proportions approximating three-quarters to one and one-quarter pounds of aluminum per ton of metal, to stop rimming action, and than allowing the ingot to completely solidify.

MICHAEL J. DEVANEY. 

